Wireless products and services have continued to expand to the point that finite resources of available communication spectrum are being overwhelmed. Industry has been forced to make dramatic changes, as it must adapt to accommodate the exponential demand on spectrum access, efficiency and reliability.
The Federal Communications Commission (FCC) in the United States, and its counterparts around the world, allocate radio spectrum across frequency channels of varying bandwidth. Various bands may cover, for example, AM radio, VH television, cellular phones, citizen's-band radio, pagers and so on. As more devices go wireless, an increasingly crowded amount of radio spectrum needs to be shared. Although the radio spectrum is almost entirely occupied, not all devices use portions of the radio spectrum at the same time or location. At certain times, a large percentage of the allocated spectrum may be sitting idle, even though it is officially accounted for. Regulatory authorities are beginning to permit usage of allocated spectrum on a secondary basis under certain strict constraints. For example, the FCC is beginning to permit the secondary usage of channels 21-51, also known as TV white space.
Cognitive radio is a term used to describe a suite of technologies with the potential to significantly alter the manner in which spectrum is utilized by future radio systems. A paradigm for wireless communication in which either a network or wireless device alters its transmission or reception parameters to avoid inference with licensed or unlicensed incumbent users, cognitive radio implements measures to avoid selecting an occupied frequency, so as to avoid interference that can possibly damage the incumbent device and/or reduce its signal reception quality. The alteration of parameters is based on active monitoring of several factors in the external and internal radio environment, such as radio frequency usage, user behavior and network state. Cognitive radio operation in TV White Space is strictly conditional on reliable detection of occupied and unoccupied spectrum and is also conditional on fast network recovery in the case of in-band incumbent detection.
Attempts to detect an incumbent system have included the use of sensing techniques. Despite advances in sensor technologies, no single sensor is capable of obtaining all the required information reliably, at all times, in often dynamic environments, such as public safety environments including firefighting, law enforcement and search and rescue to name a few. Moreover, the varying degrees of uncertainty inherent in a sensor system and the practical reality of occasional sensor failure, results in a lack of confidence in sensor measurements. This lack of confidence in single sensor systems has led to the use of co-operative sensing techniques capable of utilizing the distributed sensing gain. The disadvantages associated with past cooperative sensing techniques have historically been: delay in decision; excessive use of control channel bandwidth; and the inability to accurately identify malicious nodes.
Accordingly, it is highly desirable to implement a CR network having optimized spectrum sensing management and control in a cognitive radio network.
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